November_EDFA_Digital

edfas.org 5 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 19 NO. 4 Fig. 2 Oscilloscope plot of the input/output signals Fig. 3 Simplified design of the overvoltage/undervoltage protection function Fig. 4 Identification of the test points on a virtual slice obtained by x-ray CT Fig. 5 Local probing results (output of the comparator in green) device. Cracks were detected on four pins located on the same side of the component. Of course, this defect could have been seen from the beginningof the failureanalysisprocess. X-ray imaginghad been performed at the start, but it is almost impossible to find the defect when one does not knowwhere to look for it. Also, x-ray images are tricky to read, because the device is a superposition of two double-sided PCBAs. The same defect was found on other nonfunctional DC/DC converters.